An engine mount is disposed between a vehicle body and an engine to support the engine and serves to reduce noise and vibrations which are transmitted from the engine into a room of a vehicle through the vehicle body. In addition, excessive vibration of the engine such that the engine shakes by resonance according to a mass of the engine and rigidity of the mount occurs due to road vibration excitation when the vehicle travels. The mount, thus needs to be designed to secure high attenuation performance at the resonance frequency in order to reduce excessive vibration.
That is, the engine of the vehicle or a power plant including the engine and a transmission is supported in the vehicle body by interposing therebetween the mount having a function of suppressing vibration and noise. For this function of preventing vibration and noise, recently, a liquid sealed mount sealed with a fluid having viscosity is widely used.
The liquid sealed mount has a fluid chamber, enclosed by a main rubber plate and bellows, is separated into an upper fluid chamber and a lower fluid chamber by operating plates and a plate having an annular passage. When vibration is occurs from the engine, volume of the upper fluid chamber is varied as a main rubber (insulator) is deformed, an amount of the fluid corresponding the varied volume is moved from the upper fluid chamber to the lower fluid chamber, and at this time, the fluid flows along the annular passage or in a free gap between the operating plates.
If the amount of the fluid corresponding to the deformed volume of the main rubber is larger than the amount of fluid flowing between the free gap between the operating plates (that is, when a low frequency and large displacement vibration is transmitted from the engine), the fluid flows along the annular passage without passing through the gap between the operating plates, and at this time, the fluid in the annular passage generates resonance at a particular frequency, thereby transmitting a high attenuating force to the engine.
However, there are drawbacks such as an output is decreased and fuel efficiency deteriorates due to increase in overall weight of the vehicle because cost of the liquid sealed mount and manufacturing costs for the vehicle are excessively high, and the liquid sealed mount is heavy. Accordingly, a less expensive and lighter air damping mount has been developed recently.
However, the air damping mount is restricted for a limited degree of freedom in design because an amount in which the vibration is attenuated and a frequency at which maximum attenuation occurs are simultaneously varied in accordance with size of an air hole through which air flows.
Recently, as improvement in fuel efficiency has been emphasized as an important factor for developing vehicles, a representative engine such as a carbon dynamic airbox (CDA) engine has been introduced. The CDA engine stops a part of cylinders when the vehicle travels at a constant speed except for a case in which a large amount of torque is necessary, thus considerably improving fuel efficiency.
Nevertheless, since a high vibration occurs at the time of stopping engine with deterioration of noise, vibration, and harshness (NVH) of the vehicle, commercializing the CDA engine is difficult. To solve this problem, a technology of active engine mounting has been developed.
The engine mount serves to autonomously produce force and offset the vibration in a case in which a large vibration occurs in a CDA operation section. There are various active mounting structures, but an electronic or electric active mounting to be applied to the CDA is generally used which may produce vibration exciting force with a phase difference.
Electronic active mounting is used to perform control using one electromagnet, and may attenuate vibration at a particular frequency only. The electric active mounting is capable of attenuating vibration at all the frequencies having one electromagnet, and one permanent magnet thereby has better performance than the electronic active mounting.
The electronic active mount attenuates only a particular frequency by performing unidirectional control, but the electric active mount is capable of performing bidirectional control by using an additional permanent magnet and has characteristics of attenuating multiple frequencies.
However, because the additional permanent magnet is made of a rare earth material, supply and demand thereof are unstable, cost thereof is high, and weight thereof is large. As a result, utilizing a permanent magnet can be problematic.